An aqueous adhesive mixture with a poly(meth-)acrylate base is described in German Patent Document DE-OS No. 34 07 270. This adhesive is used in the production of a self-adhesive foil with which it is possible to protect sensitive surfaces, for example, lacquer-coated synthetic resin structural shapes during transport, storage and conditioning. The adhesive is available as a cloudy aqueous dispersion and cannot be used effectively to bond surfaces together regardless of the material from which they are constituted and thus can not be termed "universal adhesive". The term "universal adhesive" is used to refer to an adhesive which can be used to bond flexible or rigid, porous or nonporous, metallic, glass, wood, fabric, paper, leather and other materials together upon an application of the adhesive to one or both surfaces and then pressing of the surfaces together.
It is true that a "universal adhesive" as this term is used here cannot be used to bond every pair of materials together, since there are substrates or materials to be bonded to which the adhesive will not adhere and which will be repellant to or damaged by the adhesive. Nevertheless, there are enough substrates and materials with mutually different term is considered applicable. The "universal adhesive" is probably better described as a multipurpose adhesive, for this reason, but both terms may be used interchangeably here and we will continue to use the term "universal adhesive" because this term has received an art recognized significance for an adhesive capable of bonding many different materials to themselves and other materials.
Universal adhesives as have been provided heretofore contain high-molecular-weight compounds as the adhesive substance which can bond to many surfaces. Preferred high molecular weight compounds for this purpose heretofore have been nitrocellulose and polyvinylacetate. These materials are contained in solvent mixtures which might consist, for example, of esters and ketones and in many cases may also have significant proportions of alcohols.
The composition of the solvent and the solvent proportion are determined by the polymers used, the desired flowability (rheological) properties of the adhesive and the requisite bonding velocity. On certain synthetic resins or plastics, the solvent can have a solubilizing or attacking effect.
Typical of the substrates which may be bonded to or which may be bonded to another substrate are wood, paper, metal, leather and the like. Commercially available universal adhesives include UHU, PRITT and STABILIT universal adhesives.
As has already been indicated, these known universal adhesives contain high proportions of organic solvents. In general, this is a disadvantage because the solvents are environmentally hazardous and create dangerous and unhealthy conditions in the workplace. Frequently, the adhesives must be diluted or thinned with the organic solvent which thus must be handled even apart from the adhesives, or the solvent is evaporated at the workplace and the vapors may not be fully carried off in a safe or healthy manner.
There are, of course, known aqueous universal adhesives which avoid these drawbacks. However, in the presence of moisture the bonded adhesive tends to redisperse so that a permanent bond of the substrates joined together cannot exist, i.e. the bond may separate. In addition, the tensile and shear strengths of the adhesive bonds formed with these aqueous systems are generally not satisfactory.
Furthermore, in many cases it is desirable that the universal adhesives be transparent and this requirement is not fulfilled by most of the commercial aqueous universal adhesives currently available.